Figure REF  shows instantaneous snapshots of the near wake of a spheroid and a disk at \(\mbox{\textit {Fr}}= 2\)  and \(\mbox{\textit {Fr}}= 10\) . At both \(\mbox{\textit {Fr}}\) , the near wake structure of the two bodies is very different. Compared to the spheroid with turbulent boundary layer (TBL), the disk wake has a large recirculation region (\(\sim 2D\) ), as shown by the red isolines in figure REF . This large recirculation region oscillates [1]} and generates a vortex shedding structure that is advected downstream [2]}. In a spheroid with TBL, the recirculation region is very small (\(\sim 0.1D\) ) and is surrounded by the small scale turbulence of the boundary layer. As a result, the near wake is highly organized and large-scale oscillations are not observed in the near wake [3]}, [4]}, [5]}. Only further downstream, does the wake begin to show a helical structure. This change in the structure of the slender body wake has been found to lead to a change in the decay rate and dissipation scaling in the unstratified wake (ONS21). In the following sections, we will analyze how the differences between the near wake of a disk and that of a spheroid lead to distinct trends of mean and turbulence evolution in a stratified environment. But first, let us describe different snapshots of the spheroid intermediate and far wakes. Snapshots of the disk intermediate and far wakes can be found in CS20.
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